WO95/29171 discloses the preparation of arthropocidal oxadiazines from dicarboxylate oxadiazines of Formula I and hydrazine carboxylates of Formula II.
In WO95/29171, compounds of Formula I are prepared by reacting compounds of Formula II with a di(C.sub.1 -C.sub.3 alkoxy)methane in the presence of a Lewis acid, optionally in an inert solvent. The Lewis acids named are P.sub.2 O.sub.5, BF.sub.3, SO.sub.3 (0.9 to 4.0 molar equivalent required) and metal trifluoromethanesulfonates (0.1 to 0.5 molar equivalent required). All of the specifically named solvents for this transformation are halogenated (dichloromethane, 1,2-dichloroethane, chlorobenzene, a,a,a -trifluorotoluene). It is stated that when a metal trifluoromethanesulfonate is employed, it is preferable to continuously remove the byproduct alcohol by distillation. In contrast, the process of the present invention allows for the use of a protic acid such as para-toluene sulfonic acid in catalytic quantities, such as 0.1 molar equivalent in a non-halogenated solvent (e.g. toluene) to provide good product quality in high chemical yield.
The need exists for a more efficient process to prepare oxadiazines of Formula I from hydrazine carboxylates of Formula II.